Electric resistance grid



Oct. 2, 1945 L. SATCHWELL ELECTRIC RESISTANCE GRID Filed June 12, 1943 2Sheets-Sheet l ow Mz, M

L SATCHWELL 2,386,065

Oct. 2, 1945.

' ELECTRIC RESISTANCE GRID Filed June 12, 1943 2 Sheets-Sheet 2 [Lfi rfnPatented Oct. 2, 1945 UNITED STATES PATENT OFFICE ELECTRIC RESISTANCEGRID Leonard Satchwell, Marlow, England Application June 12, 1943,Serial No. 490,566 In Great Britain June 27, 1942 20 Claims.

The present invention relates to electric resistance grids.

Due to the inherently low specific resistance of common metals it hasalways been necessary to construct resistances by dividing or rollingmetals into long paths and finally bending such long paths of metal intoa series of coils or convolutions known as grids in such manner that asufficient length of metal is contained within a compact cubic formwhile preserving air spaces between parallel lying portions of the pathso that heat produced in the resistance may be dissipated by convection.

It is well known that mechanical weakness results from the form ofconstruction referred to and determines the minimum spacing of the turnsor convolutions of the metal if touching together of such turns orconvolutions is to be avoided.

To overcome this disadvantage and to produce rigidity in such resistancegrids it has been proposed to pass insulated supports through all theturns or every few turns or bars of the grids so as to clamp each bar orevery few bars of the grid rigidly to prevent swagging and touching ofadjacent turns or grids.

These methods of adding to the rigidity of the structure, apart frombeing costly, usually result in some part of the current carryingcircuit being enclosed by the insulated supporting or stiffening meansadversely afiecting dissipation of heat from the part so enclosed.

One object of the present invention is to provide a construction ofelectric resistance grids whereby rigidity may be added to grids in suchmanner that no part of the resistance grid itself is affected thermallyby the stiiTening means. A further object of the invention is to providemeans whereby terminals can be provided on the grids Which terminals areanchored to positions which are sufiiciently rigid to permit boltedconnections to be made with safety.

In accordance with the present invention some of the bars of theelectric resistance grid are provided with struts formed thereon orsecured r thereto and extending beyond the grid proper for atttachmentto stifiening or supporting members. Some of such struts are suitablyformed to provide for tapping connections or to act as terminals at theends of the grids. In resistance grids formed of a pair of spaced gridelements the struts suitably extend into the space between the gridelements and are anchored to a common stifiening or supporting member insuch space.

The invention is illustrated in the accompanying drawings in which Fig.1 is a perspective view of a resistance grid showing the inventionapplied to an arrangement of a pair of oppositely disposed grid elementseach comprising a plurality of individual flat metal grid bar-s formedby stamping with oppositely extended bosses at the ends of the bars withthe adjacent bosses of successive bars welded, brazed or solderedtogether to form a grid of substantially zigzag form somewhat asdescribed in my copending application for patent, Serial No. 487,142.

Figs. 2, 3, 4 and 5 are views of different integers of a grid such asshown in Fig. 1 while Fig. 6 is a plan view of a typical arrangement ofa number of resistance grids constructed as shown in Fig. 1 mounted on asupporting framework.

In the arrangement shown in Fig. l, the resistance grid is made up of apair of grid elements some of the bars A of each of which are providedin accordance with the invention with struts b which extend outside theboundaries of the grid proper from about midway of the length of thebar. These struts b are anchored to stiffening or supporting membersconstituted by tie rods a which are in the form of insulated rods ortubes, the struts extending from the grids having pierced holes suitablyarranged for assembly on such tie rods. Fig. 2 shows one bar of a gridsuch as is shown in Fig. 1 and shows two pierced holes b for the passageof thetwo tie rods :1, a of Fig. 1.

As shown in ,Fig. 1 some of the struts b are provided with extendingportions 0 serving as tapping connections as shown in Fig. 3 also whilein others the grid bar are provided with lugs e which serve as terminalconnections as shown also in Fig. 4. In order to avoid the necessity ofcoverin the supporting rods with insulating material where such rodsreceive the struts threaded upon them the struts themselves may carryinsulating means and a preferred form is shown in Fig. 5 wherein themetal around the holes I) of the struts is provided with embossments b"which form seatings for mica or like washers m, the internal diameter ofwhich is less than that of the holes b. The mica or like washers m arealigned by the embossments b" and serve to position metal bushes orferrules o secured thereon which serve to support the tie rods. As willbe seen the mica or like washers m being of smaller internal diameterthan the holes I) provide an air gap between the bushes or ferrules oand the struts. The tie rods in such circumstances do not require to beinsulated as the strut carries its own insulation.

The number of struts provided for each grid will depend upon the lack ofrigidity in a particular section of grid. If the grid bar is of largecurrent carrying capacity and therefore of relatively large section itwill not require as many struts as a grid used for weaker currents whichwill have a smaller section of metaland therefore less rigidity.

A number of electric resistance grids, such as shown in Fig. 1, areshown in Fig. 6 mounted in a supporting framework (1 and the strutformation is indicated in a representative case. The electric resistancegrids are provided with brackets h secured to the tie rods (1, thebrackets it being adapted for fixing on insulated support rods 70 whichrods normally carry a number of resistance rids. The grids are shown asconnected into continuous circuit by connection of the terminals 6.

I claim:

1. An electric resistance grid of zigzag form with parallel bars,stiffening members, some of said bars formed with integral projectionsextending from the grid proper transversely of the plane thereof forattachment to the stiffening members whereby to improve rigidity, andsome of said projections having extended portions arranged to providetapping connections.

2. An electric resistance grid of zigzag form with parallel bars,stiffening members, some of said bars having integral projectionssecured thereto and extending from the grid proper transversely of theplane thereof for attachment to the stiffening members whereby toimprove rigidity, and some of said projections naving extended portionsarranged to provide tappin con nections.

3. An electric resistance grid of zigzag form with parallel bars,stiifening members, some of said bars formed with integral projectionsextending from the grid proper transversely of the plane thereof forattachment to the stiffening members whereby to improve rigidity, andsome of said projections having lugs extending therefrom and servin asterminal connections.

4. An electric resistance grid of zigzag form with parallel bars,stiffening, members, some of said bars having integral projectionssecured thereto and extending from the grid proper transversely of theplane thereof for attachment to the stiffening members whereby toimprove rigidity, and some of said projections having lugs extendingtherefrom and serving as terminal connections.

5. An electric resistance grid of zigzag form with parallel bars,stiffening members, some of said bars formed with projections, saidprojections extending transversely of the plane of the grid proper forattachment to the stiffening members, said projections being formed withholes and with embossments around the holes, a pair of insulatingWashers for each hole of smaller internal diameter than the holes, atleast one of which about each hole seating in and retained by saidembossments, and ferrules extending through the holes and washers andinsulated from the projections by said washers, the stiffening membersextending through the ferrules and the washers presenting an air gapbetween the projections and the ferrules whereby non-insulatedstiffening members may be used.

6. An electric resistance grid of zigzag form having parallel bars,stiffening members, some of said bars having projections securedthereto, said projections extending transversely of the plane of thegrid for attachment to the stiffening members said projections beingformed with holes and with embossments around the holes, a pair ofinsulating washers for each hole of smaller internal diameter than theholes, at least one of which about each hole seatin in and retained bysaid embossments, ferrules extending through the holes and washers andinsulated from the projections by said washers, the stiffening membersextending through the ferrules and the washers presenting an air gapbetween the projections and the ferrules, and tapping connectionsintegral with the projections and commonly insulated from the stiffeningmembers, whereby non-insulated stiffening members may be used.

'7. An electric resistance grid formed of individual flat grid barshaving integral projections extending from their faces adjacent theirends and welded to adjacent bars to provide a substantially zigzag form,stiffening members, some of said bars provided with struts extendingfrom the grid proper for attachment to the stiffening members whereby toimprove rigidity.

8. An electric resistance grid formed of individual fiat grid barshaving integral projections extending from their faces adjacent theirends and brazed to adjacent bars to provide a substantially zigzag form,stiffening members, some of said bars provided with struts extendingfrom the grid proper for attachment to the stiffening members whereby toimprove rigidity.

9. An electric resistance grid formed of individual flat grid barshaving integral projections extending from their faces adjacent theirends and soldered to adjacent bars to provide a substantially zigzagform, stiffenin members, some of said bars provided with strutsextending from the grid proper for attachment to the stiffening memberswhereby to improve rigidity.

10. An electric resistance grid formed of a pair of spaced flat gridelements of zigzag form each comprising individual metal bars havingintegral projections extending from their faces adjacent their ends andwelded to adjacent bars, stiffenin members, said bars having strutsintegral with some of the grid bars extending into the space between thegrid elements, said struts adapted to be anchored to a common stiffeningmember.

11. An electric resistance grid formed of a pair of spaced fiat gridelements of zigzag form eacn comprising individual metal bars havingintegral projections extending from their faces adjacent their ends andbrazed to adjacent bars, stiff ening members, said bars having strutsintegral with some of the grid bars extending into the space between thegrid elements, said struts adapted to be anchored to a common stiffeningmember.

12. An electric resistance grid formed of a pair of spaced flat gridelements of zigzag form each comprising individual metal bars havingintegral projections extending from their faces adjacent their ends andsoldered to adjacent bars, stiffening members, said bars having strutsintegral with some of the grid bars extending into the space between thegrid elements, said struts adapted to be anchored to a common stiffeningmember.

13. An electric resistance grid formed of individual grid bars welded toether adjacent their ends to provide a substantially zigzag form,stiffening members,.sorne of said bars provided with struts extendingfrom about midway of the length of the grid bars for? attachment toStifi-r ening members whereby to improve rigidity.

14. An electric resistance grid formed of individual grid bars brazedtogether adjacent their ends to provide a substantially zigzag form,stiff ening members, some of said bars provided with struts extendingfrom about midway of the length of the grid bars for attachment tostiffening members whereby to improve rigidity.

15. An electric resistance grid formed of individual grid bars solderedtogether adjacent their ends to provide a substantially zigzag form,stiffening members, some of said bars provided with struts extendingfrom about midway of the length of the grid bars for attachment tostiiT- ening members whereby to improve rigidity.

16. An electric resistance grid formed of a pair of spaced grid elementsof zigzag form each comprising individual metal bars welded togetheradjacent their ends, stiffening members, some of said bars having strutsintegral therewith extending from about midway of the length of the gridbars into the space between the grid elements, said struts being adaptedto be anchored to a common stiffening member.

17. An electric resistance grid formed of a pair of spaced grid elementsof zigzag form each comprisin individual metal bars brazed togetheradjacent their ends, stiffening members, some of said bars having strutsintegral therewith extending from about midway of the length of the gridbars into the space between the grid elements, said struts being adaptedto be anchored to a common stiffening member.

18. An electric resistance grid formed of a pair of spaced grid elementsof zigzag form each comprising individual metal bars soldered togetheradjacent their ends, stiifening members, some of said bars having strutsintegral therewith extending from about midway of the length of the gridbars into the space between the grid elements, said struts being adaptedto be anchored to a common stiffening member.

19. An electric resistance grid formed of individual grid bars weldedtogether adjacent their ends to provide a substantially zigza form,stiffening members, some of said bars provided with struts provided withattached insulation and extending from about midway of the length of thegrid bars for attachment to stiiTening members whereby to improverigidity.

20. An electric resistance grid formed of a. pair of spaced gridelements of Zigzag form each comprising individual metal bars weldedtogether adjacent their ends, stiffening members, some of said barshavin struts integral therewith with attached insulation and extendingfrom about midway of the length of the grid bars into the space betweenthe grid elements, said struts being adapted to be anchored to a commonstifiening member.

LEONARD SATCHWELL.

